1. Field of the Invention
The present invention relates to the stabilization of anhydrous sodium metasilicate and, more especially, to the stabilization of anhydrous sodium metasilicate by formulating same with certain water evolving additives as will release molecular water thereto; thus converting a minor proportion of the anhydrous metasilicate into its pentahydrate form.
2. Description of the Prior Art
Sodium metasilicate is a commercially valuable salt highly useful in the manufacture of soap and various detergent compositions, imparting thereto the required alkalinity while at the same time being less caustic than the otherwise comparable alkaline salts. In particular, in spite of its alkalinity sodium metasilicate is far less corrosive to glass and such light metals as aluminum.
Furthermore, this salt is a highly advantageous emulsifying agent for detergent compositions and too is characterized by the ability to firmly resist redeposition.
Also, it is widely used in detergent compositions intended for household washing, e.g., for the washing of kitchen utensils and glass- and tableware. Such detergent compositions typically contain nonionic surface active agents which reduce the surface tension of the wash water, thus reinforcing the detergent and more readily emulsifying any fats. As examples of the surface active agents typically comprising the known detergents, there are noted those surfactants resulting from the condensation of ethylene oxide and a polypropylene glycol, or of ethylene oxide and alkyl phenols.
Unfortunately, however, those compositions formulated from an admixture of the aforementioned ingredients and of anhydrous sodium metasilicate are not stable. Specifically, such compositions are subject to coloration after but a limited period of storage time, and, not uncommonly, the evolution of a perfume-like odor is detected, especially when the compositions comprise aldehyde bases.
It too will be appreciated that the problematical "inversion" temperature of such compositions varies as a function of time. The "inversion" temperature is defined as that temperature, above which an aqueous solution of said composition becomes heterogeneous by phase separation into two liquid phases; this separation effects deleterious variation in the hydrophilic/lipophilic balance of the surface active agent.
Another problem ascribable to anhydrous sodium metasilicate is that it causes respiratory problems in users thereof. These respiratory problems (nasal irritation, sneezing, etc.) are due to the inhalation of the very fine metasilicate powder or dust which results from the wear or attrition of the larger particles sizes during the various mechanical manipulations encountered on use of the product. The term "dusting" is used herein to describe this phenomenon.
It too has already been proposed to stabilize this metasilicate by treating it with certain gluconic derivatives, as described in U.S. Pat. No. 4,031,024, e.g., by treatment with gluconic acid or with the water soluble sodium salts thereof, or with certain derivatives of phosphorus, as described in U.S. Pat. No. 3,996,399, e.g., by treatment with monosodium phosphate. From a practical point of view, however, such treatments require the use of a liquid medium which necessitates pulverization. Treatment with a liquid is required because the objective is to reduce attrition and "dusting".